class_docstr: Feature Pyramid Network as described in `"Feature Pyramid Networks for Object Detection"
  <https://arxiv.org/pdf/1612.03144.pdf>`_.
  
  Args:
  ----
      channels: number of channel to output
code: def extra_repr(self) -> str:
      return f"channels={self.channels}"
  
imports: from copy import deepcopy
  from typing import Any, Dict, List, Optional, Tuple
  import numpy
  import tensorflow
  from tensorflow import keras
  from tensorflow.keras import layers
  from tensorflow.keras.applications import ResNet50
  from doctr.file_utils import CLASS_NAME
  from doctr.models.utils import IntermediateLayerGetter, _bf16_to_float32, conv_sequence, load_pretrained_params
  from doctr.utils.repr import NestedObject
  from ...classification import mobilenet_v3_large
  from .base import DBPostProcessor, _DBNet
label_desc: Use image node_id 3 for calling the FeaturePyramidNetwork obj's underlying member method code with example usage: obj.extra_repr() and returns: str, self